I was just listening to the John Harris interview on The Ralph Bristol Show. During that interview John was discussing the "what ifs" had the Martin/Zimmerman situation had happened here.
John talked about a case here in Tennessee where someone was forced to defend his life with a gun. The bad guy was shot three times. When all was said and done, the good guy was charged and convicted of - if I remember correctly - homicide. The courts felt, based on Tennessee law, the good guy shot the bad guy too many times. According to John, you are allowed to shoot the bad guy only as many times as necessary to stop the threat.
John didn't have time to go into great detail about the case, but 3 shots doesn't sound excessive to me. Unless they can prove you shot the bad guy enough to stop the threat, then stood over his body and pumped another round or two into him just for good measure, who's to say how many is too many?
I guess a situation like this affirms the importance of proper shot placement.